Whether you're a footwear designer or just interested in how the human body works, you should watch this.
First, a preamble: I've been training in internal martial arts for years and teach qi gong to private clients on the side. Both of these things have taught me that that most of us sit, stand, walk, carry things and even breathe incorrectly, in ways that are ultimately detrimental. Most of you reading this probably have some sort of back, shoulder or knee problems, and they'll worsen over time.
Here's why: We are born with correct posture and movement instincts—and almost immediately learn bad physical habits. Babies are sat in high chairs, children are sat at school desks for hours and saddled with backpacks before and after. We walk around on unforgiving concrete and wear artificially spongy shoes to compensate. All of these things promote habits of incorrect posture that last for the rest of our lives and cause stiffness, soreness or outright injury.
These unnatural trappings even lead us to breathe incorrectly; very young children naturally breathe into their diaphragms, which is correct. But unless you take yoga or something similar, I'm willing to bet most of you reading this breathe into your chests.
Sorry for the long aside. In this video, Cornelius Berthold of Germany's History Park Bärnau—a sort of Colonial Williamsburg, but Slavic and medieval—explains how we used to walk very differently, due to the more naturalistic design of old-school footwear:
It makes total sense to me. If you've ever been at one of those lousy unsandy beaches where you need to walk across sharp rocks while barefoot, you'll recognize that in that situation you walk exactly as Berthold demonstrated.
I should point out that in the internal martial art of Ba Gua a form of walking called "mud stepping," similar to what Berthold demonstrated, is practiced and drilled. If you ever have an opportunity to try it, you'll find that it engages completely different muscle groups than our modern-day walking style does. It also places your spine into the correct natural alignment.
I'm not sure exactly what modern-day footwear designers could do that could get us to walk the way Berthold shows. But if anyone from Nike, Adidas etc. is reading this, I can tell you there is a desperate need for someone to design a proper kung fu/Tai Chi slipper with characteristics very different from modern-day sneakers. Drop a line and I'll tell you all about it.